Efficient method and apparatus for generating singlet delta oxygen at an elevated pressure

ABSTRACT

An improved singlet delta oxygen generator (SOG) and method of its use are disclosed. The improved SOG is compact and scalable, capable of operating in a zero-gravity or low gravity environment, requires no gaseous diluent or buffer gas, and is capable of operating at pressures as high as one atmosphere. The improved SOG also efficiently utilizes the reactants and produces a O 2 ( 1 Δ) stream that is largely free of chlorine and water vapor contamination and therefore does not require a BHP regeneration system or a water vapor trap. When used as part of a COIL system, the SOG may be part of a plenum that directly feeds the laser&#39;s nozzle. The close proximity of the SOG to the laser cavity allows operation of the SOG at higher pressures without significant depletion of available O 2 ( 1 Δ) through collisional deactivation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/453,148, entitled “EFFICIENT METHOD AND APPARATUS FOR GENERATINGSINGLET DELTA OXYGEN AT AN ELEVATED PRESSURE” filed on Jun. 3, 2003,which claims priority to U.S. Provisional Application Ser. No.60/387,539, filed on Jun. 10, 2002.

TECHNICAL FIELD

The present invention relates generally to an improved method andapparatus for generating electronically excited states of oxygen withincreased efficiency and at an elevated pressure.

BACKGROUND OF THE INVENTION

The invention relates to an improved method and apparatus for generatingthe singlet delta electronically excited state of diatomic oxygen,O₂(a¹Δ_(g)), in vapor form. The apparatus for generating singlet deltaoxygen is referred to as a singlet oxygen generator or SOG. Singletdelta oxygen is most typically used in chemical lasers, or specificallyin chemical oxygen-iodine lasers (COIL), although there may be otheruses for singlet delta oxygen and particularly for singlet delta oxygengenerated according to the method and using the SOG of the invention.

Singlet delta oxygen is generally produced by reacting aqueous basichydrogen peroxide (BHP) with chlorine. Aqueous BHP is produced by mixingliquid water with an aqueous solution of hydrogen peroxide (H₂O₂) and anaqueous solution of potassium hydroxide (KOH). Alternatively, sodiumhydroxide (NaOH) may be used in place of KOH. In the BHP solution, theH₂O₂ and KOH exist as various ionic molecules. The mixing and reactiveprocess in making BHP is exothermic.

When BHP is mixed with chlorine, the following stoichiometric chemicalreaction takes place:H₂O₂+2KOH+Cl₂→2KCl+2H₂O₂   Reaction Awhere the oxygen is in its lowest energy electronically excited state,O₂(a¹Δ_(g)). For convenience, this is referred to as singlet deltaoxygen or as O₂(¹Δ). Normally, oxygen is in its electronic ground state,O₂(X³Σ g), which, hereafter, is written as O₂(³Σ) or just O₂. InReaction A, the chlorine vapor diffuses into the aqueous BHP solution,forming potassium chloride (KCI), or sodium chloride (NaCl) if NaOH isused in the reaction, water, and O₂(¹Δ). The O₂(¹Δ) can form bubbles anddiffuse out of the solution. The presence of singlet delta oxygen fromthe reaction of BHP and chlorine in Reaction A is evident by a red dimolemission (see “Direct Spectroscopic Evidence for a Deuterium SolventEffect on the Lifetime of Singlet Delta Oxygen in Water,” Kajiwara andKearns, Journal of the American Chemical Society, vol. 95, No. 18, pp.5886-5890, September 1973) that is visible by sight. This emission stemsfrom the chemiluminescence of (O₂(a¹Δ))₂.

Singlet delta oxygen has a long radiative lifetime of about 90 minutes,but can collisionally deactivate in much less time, resulting in theproduction of the ground state and the next higher electronicallyexcited state, O₂(¹Σ), of diatomic oxygen. An important process is thegas-phase pooling reaction:O₂(¹Δ)+O₂(¹Δ)

O₂(³Σ)+O₂(¹Σ)   Reaction Bwherein O₂(¹Σ) is shorthand for O₂(b¹Σ⁺ _(g)), which is a more energeticelectronic state than singlet delta oxygen. The O₂(¹Σ) and O₂(³Σ) arecontaminants or byproducts in the singlet delta oxygen stream, whichreduce the yield of singlet delta oxygen. When O₂(¹Δ) is the preferredproduct, as is the case with the chemical laser, then Reaction B is adeactivation process to the extent that the forward rate exceeds thebackward rate.

Reaction B is a gas-phase process that can be viewed as producing theO₂(¹Σ) state. In non-laser applications, this state may be preferred asequal to or superior to the O₂(¹Δ) state. Hereafter, when discussing thesinglet delta state of oxygen, as generated by an SOG according to theinvention, the O₂(¹Σ) state, produced by Reaction B, is not excluded.

An important deactivation process is the dimol reaction:O₂(¹Δ)+O₂(¹Δ)→(O₂(a¹Δ))₂  Reaction CReactions B and C are the primary deactivation process for removingO₂(¹Δ) in the gas phase. The gas phase generated by the SOG of thisinvention consists of O₂(¹Δ) (which is the preferred species for COIL),O₂(³Σ), O₂(¹Σ), H₂O, and possibly a small mole fraction of chlorinevapor. The O₂(³Σ), O₂(¹Σ), H₂O and chlorine vapor (if any) are referredto as the gas-phase byproducts. In addition, there may or may not beadded diluent, which is not a byproduct. For COIL, a common measure ofeffectiveness is the yield, which is the mole ratio of O₂(¹Δ) divided bythe total oxygen.

Various types of singlet delta oxygen generators have been developed inthe prior art. These generators typically use BHP with chlorine and adiluent gas, such as helium. Optimum singlet delta oxygen productionoccurs when the H₂O molar flow rate, relative to the KOH, or NaOH, molarflow rate is about double that suggested by Reaction A; i.e., H₂O₂ andKOH have approximately the same molar flow rate. These molar flow rateswere used in the feasibility experiment according to the invention, asdescribed later.

One type of prior art SOG uses a transverse flow uniform droplet methodin which BHP droplets, ranging in size from 0.4 mm to 0.5 mm (15.8 milto 19.7 mil) diameter, fall under the influence of gravity into a sump.Chlorine vapor and a diluent gas flow across the path of the droplets.The flow speed of the chlorine vapor and diluent is limited, otherwisethe droplets would be transported downstream with the diluent and thegenerated oxygen. There is an adverse trade-off in that the maximumvapor speed, which includes the generated singlet delta oxygen, mustdecrease as the droplet size decreases. Generator pressures of around 92Torr (0.12 atm), most of which is due to helium diluent, have beenreported in this type of SOG. The partial pressure of the generatedoxygen reported for this type of SOG is only around 14.3 Torr (0.02atm).

Another type of prior art SOG is a verticoil oxygen generator. In thisdevice, a number of disks rotate such that the lower portion of thedisks is in a BHP sump. The upper portion of the disks is thus wettedwith a BHP film. Chlorine vapor and diluent flow past the upper part ofthe disks to react with the BHP film. Generator pressures of about 40Torr (0.05 atm), most of which stems from the helium diluent that entersthe reactor with the chlorine vapor, have been reported in this type ofSOG.

Another type of prior art SOG is a twisted-flow aersol-jet singletoxygen generator. A partial pressure of about 75 Torr (0.1 atm) ofsinglet delta oxygen has been reported for this type of generator, butthis O₂(¹Δ) pressure decreases, to around 22.5 Torr (0.03 atm), at anozzle inlet for a laser. This significantly decreases the laserefficiency.

The foregoing prior art SOGs have, in common, a number of adversecharacteristics:

(a) The devices are bulky, and typically require ducting to transportthe O₂(¹Δ) stream to the nozzle that feeds the laser cavity. Thesedevices are not well suited for scaling a laser module to a high-powerlevel.

(b) Primarily, because of Reactions B and C, the singlet delta oxygenpartial pressure entering the inlet of the laser's nozzle has notexceeded about 22.5 Torr (0.03 atm) in prior art systems. To increasethe plenum pressure of the laser's nozzle, a diluent gas is used,typically helium or nitrogen. The need for supply tanks, plumbing, etc.,to accommodate the use of a diluent gas further increases the size andweight of the overall system.

(c) The devices have difficulty keeping water vapor and water dropletsfrom being entrained in the singlet delta oxygen stream. Water vapor isa deactivator that reduces the laser's performance. In many prior artsystems, a water vapor trap and liquid separator, located between theSOG and laser nozzle, are needed. These traps, however, reduce thesinglet delta oxygen concentration that enters into the laser's nozzle.

(d) Only a small percentage of the reactive chemicals in the BHPsolution are utilized as the BHP flows through the oxygen generator.This results in a large and heavy BHP feed system, or a large and heavysystem to recondition or regenerate the partly spent BHP.

(e) As described in “Mixed Marks for the ABL,” by Canan in AerospaceAmerica, pp. 38-43, August 1999, Earth's gravitational field is requiredto provide buoyancy for separating the oxygen vapor from the liquid.Prior art SOG devices that rely on gravity for separation of singletdelta oxygen from the reactant flow, or that rely on gravity forreactant flow, such as the BHP droplets which fall by force of gravityin a transverse flow uniform droplet SOG, are not suitable for operationin a space environment.

(f) Prior art systems do not appear to yield a chemical efficiency forthe laser above about 30%.

In addition to prior art SOGs, gas sparger devices are relevant to theproduction of singlet delta oxygen according to the invention and asdiscussed more fully below. Gas sparger devices are designed to removevolatile contaminants from a liquid. In a prior art gas sparger, acontaminated liquid is injected, under pressure, onto the inside surfaceof a porous tube with a circular cross section. Centrifugal force keepsthe liquid attached to the inside of the porous walled tube. The liquidfollows a helical path as it makes a number of revolutions along thewall. Air, under pressure, is injected from the outside surface of theporous walled tube, through the tube, after which it mixes with theliquid. Most of the volatile contaminants are entrained with the air,which separates from the liquid, due to buoyancy that stems from thecentrifugal force. Chemical reactions do not occur in typical gasspargers.

SUMMARY OF THE INVENTION

The present invention provides an improved method and apparatus forgenerating singlet delta oxygen. This invention is preferably used togenerate singlet delta oxygen for use in chemical lasers, but there maybe other uses for the singlet delta and singlet sigma electronicallyexcited states of oxygen. As in prior art systems, production of O₂(¹Δ)is achieved through the reaction of BHP and chlorine in a SOG accordingto the invention. A dilute basic hydrogen peroxide, or BHP, solution isproduced according to the invention by mixing aqueous hydrogen peroxide,water, and aqueous potassium hydroxide, or alternatively sodiumhydroxide or a mixture of several hydroxide compounds. The BHPproduction process is exothermic; therefore, the solution is preferablycooled during preparation and afterward.

Cooled BHP is then injected, under pressure typically greater than 400Torr, and preferably greater than about 600 Torr, into a SOG reactionchamber with a concave curved wall. At the point of entry, the solutionis a thin, high-speed, liquid layer that flows over the concave wall.The high speed of injection results in a centrifugal force that preventsthe aqueous solution from separating from the concave wall. Shortlyafter the start of the concave wall, chlorine vapor is injected, underpressure sufficient to choke the chlorine vapor flow (i.e. it approachesbecoming sonic) in the porous wall and to provide sufficient chlorinefor its reaction with BHP. The chlorine is preferably injected through aporous wall that is a small section of the concave wall. Alternatively,the chlorine may be injected under pressure through a converging,two-dimensional nozzle that terminates in a thin slit located in theplane of the concave wall. The injected chlorine vapor, in the form ofsmall bubbles, rapidly mixes and reacts with the BHP solution while theflow is still passing over the concave wall. The reaction with thechlorine produces singlet delta oxygen in a liquid, or frothy, layer.

The singlet delta oxygen forms vapor bubbles. Because of their lowdensity relative to the liquid solution, the bubbles experience asignificant pressure gradient that is transverse to the concave wall.This gradient, which is associated with the aforementioned centrifugalforce, causes the vapor bubbles to depart the aqueous solution on theside of the liquid, or frothy, layer opposite from where the chlorinevapor enters. Thus, there is little, if any, chlorine contamination inthe O₂(¹Δ) stream. As soon as most, or all, of the generated O₂(¹Δ) hasdeparted the BHP solution, the spent solution is removed from thereaction chamber by means of an outlet or exhaust duct for the liquid.

The molar flow rate of the chlorine is adjusted to maximally utilize theBHP solution with little, if any, chlorine entrained in the oxygen vaporstream. Hence, the concentrations of the active ions and molecules inthe BHP solution are significantly depleted. A BHP regenerator system isthus unnecessary.

The salt generated by the BHP-chlorine reaction remains dissolved in thehighly dilute aqueous solution. The high-speed aqueous solution passesthrough the reaction chamber very quickly. Inside the reaction chamber,the temperature of the liquid increases due to exothermic reactions withthe chlorine. Because the BHP solution contains added water and iscooled before it enters the reaction chamber, the magnitude of thetemperature increase in the reaction chamber is minimized. This factor,in combination with the reduction of the vapor pressure of the water bythe solute, and the few milliseconds that the high-speed solution islocated inside the reaction chamber, results in a low contaminationlevel of the O₂(¹Δ) gas with water vapor.

These preferred features may be used singularly or combined for theefficient generation of O₂(¹Δ) in a SOG that has a number of advantagesover the prior art, particularly when used as a source of O₂(¹Δ) for achemical oxygen iodine laser. One of these is scalability. Scalabilityis being able to extend by an arbitrary amount a single laser module inthe direction of the laser beam that circulates inside the laser cavity.These advantages thus include: (1) the SOG is compact and scalable (2)it can operate in a zero-gravity or near zero gravity environment suchas on a space satellite, (3) no added diluent or buffer gas is needed,(4) the O₂(¹Δ) may be generated at an elevated pressure, (5) thehydroxide and Cl₂ chemicals are efficiently utilized, with highpercentages of utilization, up to 100% for both, based on the known fastreaction rates, (6) the O₂(¹Δ) stream is largely free of chlorine andwater vapor contamination, and (7) the O₂(¹Δ) yield at the laser nozzlethroat is well above prior art systems and may be greater than 70%.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated into and form a part of thespecification to assist in explaining the present invention. Thedrawings are intended for illustrative purposes only and are notintended as exact representations of the embodiments of the presentinvention. The drawings further illustrate preferred examples of how theinvention can be made and used and are not to be construed as limitingthe invention to only those examples illustrated and described. In thesedrawings, the same reference characters are used throughout the views toindicate like or corresponding parts. The various advantages andfeatures of the present invention will be apparent from a considerationof the drawings in which:

FIG. 1 is a schematic diagram of a SOG system, including BHP andchlorine feed systems, as part of a plenum feeding a laser nozzleaccording to one aspect of the invention;

FIG. 2 is a cross-sectional side view of a SOG as part of a plenumfeeding a laser nozzle according to one aspect of the invention;

FIG. 3 is a schematic diagram of a SOG system, including BHP andchlorine feed systems, according to a feasibility experiment for thepresent invention; and

FIG. 4 is a cross-sectional side view of a reaction chamber of a SOGsystem according to a feasibility experiment for the present invention.

DETAILED DESCRIPTION

The following describes the preferred embodiment of a SOG system and itsmethod of use according to the present invention and according to afeasibility experiment for the present invention by reference to FIGS.1-4. Although the preferred embodiment and a feasibility experiment forthe present invention are described, the description is not intended tolimit the scope of the invention as defined by the claims. Some detailsof the SOG and chemical supply systems and their methods of use,including various gauges, fittings, piping, etc. are well known in theart, and as such are neither shown nor described. Even though numerouscharacteristics and advantages of the present invention are shown anddescribed in the drawings and accompanying text, the description isillustrative only, and changes may be made, especially in matters ofarrangement, shape and size of the parts, within the scope of theinvention to the full extent indicated by the broad general meaning ofthe terms used in the claims.

FIG. 1 is a schematic diagram of a SOG system, including BHP andchlorine feed systems, as part of a plenum wall feeding a (COIL) lasernozzle according to one aspect of the invention. The iodine feed andinjection systems for the COIL are not depicted in FIG. 1. The firststep in the overall process is the mixing of liquid water, aqueous H₂O₂and aqueous KOH in mixer tank 12. Sodium hydroxide or a mixture ofseveral hydroxide compounds may be used in place of potassium hydroxide.The resulting mixture is referred to as a basic hydrogen peroxide (BHP)solution.

In prior art systems, the H₂O₂ molar flow rate, relative to the KOH, orNaOH, molar flow rate is about double that suggested by Reaction A,i.e., H₂O₂ and KOH have approximately the same molar flow rate.Preferably, according to the invention, the H₂O₂ molar flow rate isabout 50% or more of the KOH molar flow rate, and most preferablybetween 50% to 110% of the KOH molar flow rate. The aqueous KOH andaqueous H₂O₂ mixed in mixer tank 12 are commercially available aqueoussolutions that are each buffered with additional water. Due to thisadditional water, the BHP solution is more dilute than is used in priorart systems. Although not necessarily optimum values, the mole ratios ofH₂O₂, KOH, and H₂O used in the feasibility experiment discussed belowwere approximately 1:1:10, where the H₂O molar value of 10 consists ofthe aqueous portions of the H₂O₂ and KOH solutions plus the added water.In the discussion of molar ratios of H₂O, H₂O₂, and KOH herein, the H₂Ovalue consists of the aqueous portions of the H₂O₂ and KOH solutionsplus added H₂O. The amount of dilution is higher than prior art practiceand may be further increased according to the invention to produce ahighly dilute BHP solution to aid in reaction temperature reduction.

The aqueous KOH, aqueous H₂O₂, and added water require cooling when theyare mixed because of the exothermicity of reactions. Once mixed, andsometime before usage, the BHP should be cooled to a temperature justabove its freezing point, preferably to a temperature 1° C. to 10° C.above its freezing point. This temperature is below the freezing pointfor pure liquid water, since a solute lowers the freezing point. The BHPenters SOG Reactor 14 at a temperature where its water vapor partialpressure is below the 4.6 Torr (0.006 atm) value of pure water at 0° C.Due to the use of a relatively dilute BHP solution according to thepreferred embodiment of the invention, problems in the prior art withanomalous freezing of the BHP are not encountered.

Chlorine liquid from chlorine supply tank 16 is vaporized in a heater 18with the chlorine vapor flowing into SOG 14. A pump is usually notrequired, since the room temperature vapor pressure of liquid chlorineshould be sufficient for providing the desired flow rate of chlorine toSOG 14.

The molar flow rate of the chlorine is readily adjusted to maximallyutilize the BHP solution by significantly depleting the concentrationsof active ions and molecules in the BHP solution. The molar flow rate ofchlorine is preferably slightly less than that of the KOH or NaOH.Preferably, the chlorine molar flow rate is about 80% to about 95% ofthe KOH or NaOH molar flow rate, and most preferably about 90% to about95% or more of the KOH or NaOH molar flow rate. These molar flow ratesresult in nearly 100% utilization of the KOH (or NaOH) and chlorine. Dueto the efficient utilization of the reactants, a BHP regeneration orrecycling system is not necessary according to the invention.

SOG 14 preferably includes a concave curved wall over which the BHP andchlorine are injected and react to produce singlet delta oxygen. Afterthe reaction, spent BHP solution, comprising salts, small amounts of KOHor NaOH based ions and excess H₂O₂, exits SOG 14 through exhaust outlet20 to a collection tank 22 for proper disposal. Due to the efficientutilization of chemicals according to the invention, it is not necessaryto recycle or regenerate the spent BHP solution after the reaction inSOG 14. Preferably, 90% or more of the BHP solution entering SOG 14comprises non-recycled H₂O₂ and hydroxide compounds and most preferablythe BHP solution comprises entirely new, non-recycled H₂O₂ and hydroxidecompounds. Non-recycled refers to chemicals or compounds that have notbeen recycled from the spent solution exiting SOG 14 through outlet 20.Materials recycled from other processes may be used according to theinvention.

SOG 14 is preferably part of a plenum feeding a laser nozzle 24 when SOGis used to produce O₂(¹Δ) for a COIL. A O₂(¹Δ) stream exits SOG 14through nozzle 24 to feed a laser cavity 26. Iodine feed and injectionsystems for the COIL are not shown in FIG. 1.

FIG. 2 is a cross-sectional side view of a SOG 14 as part of a plenumwall feeding a laser nozzle 24 according to one aspect of the invention.The iodine feed and injection systems for the laser are not depicted inFIG. 2. BHP and chlorine feed systems are also not depicted in FIG. 2.SOG 14 includes a reaction chamber 28 with a concave curved wall 30. Anominal radius of curvature for concave wall 30 is 2.5 cm (1 inch). SOG14 is a two-dimensional flow apparatus, the dimension of which withrespect to the plane of FIG. 2 is arbitrary. Thus, the preferredembodiment of the SOG 14 is compact and fully scalable.

BHP from mixer 12 enters reaction chamber 28 under pressure through aconverging nozzle 32 and exits the nozzle at its throat 34 at aconsiderable speed, typically in excess of 15 m/s (49.2 ft/s). The BHPsolution travels along concave wall 30 and remains in substantialcontact with this wall. At the point of entry, the BHP solution is athin, high-speed, liquid layer that may develop into a frothy layeralong concave wall 30. It is estimated that the thickness of the liquidlayer is less than about 4 mm (0.16 inches), with the frothy layer beingabout 2 to 4 times thicker than the liquid layer. It is preferred thatthe fluid layer along concave wall 30 have a thickness of 15 mm (0.6 in)or less. The solution remains a thin layer as it flows over concave wall30. The high speed of injection results in a centrifugal force thatprevents the aqueous solution from substantially separating from theconcave wall 30. The centrifugal force is quite large since the BHP is aliquid, the flow speed is large and the radius of curvature of concavewall 30 is small.

Chlorine vapor is preferably injected under pressure through a porouswall 36 that is a part of concave wall 30. The chlorine injectionprocess is regulated to avoid separating the liquid layer from theconcave wall. Alternatively, chlorine can be injected through aconverging nozzle with a throat located downstream of BHP nozzle throat34, as used in the feasibility experiment described below.

Porous wall 36 is located downstream of BHP nozzle throat 34. Mostpreferably, porous wall 36 is made from a sintered metal, such as Nickel200, or other materials, or porous plastic. It is also preferred thatthe chlorine flow through porous wall 36 chokes at the exit surface ofthe wall 36 on the interior of reaction chamber 28. A choked flowensures a nearly uniform distribution of chlorine vapor over the exitsurface of porous wall 36. It also provides useful momentum for thechlorine that will aid both the chlorine/BHP mixing and the subsequentremoval of the singlet delta oxygen from the solution. Choking alsoenables better control of the chlorine molar flow rate. The magnitude ofthe chlorine molar flow rate, which is preferably slightly less than themolar flow rate of KOH or NaOH, establishes the magnitude of the surfacearea of porous wall 36 as will be understood by those of skill in theart.

The pressure of the chlorine at the exit surface of porous wall 36 mustbe approximately equal to that of the BHP flowing along concave wall 30.Due to the centrifugal force along concave wall 30, the BHP pressure atthe wall exceeds that in a plenum. To match the BHP wall pressure, thechlorine vapor first goes through an expansion as the flow adjusts fromthe constricted flow area inside the porous wall 36 to the externalsurface of the porous wall inside reaction chamber 28. This expansionoccurs over a distance of about one average pore diameter, which can beas small as 0.2 μm (0.008 mil) or as large as 100 μm (4 mil) or larger.Before the flow exits the porous wall 36, it may go through acompression whose downstream pressure matches or approximates the BHPwall pressure. The injected chlorine vapor, in the form of smallbubbles, rapidly mixes and reacts with the BHP solution while the flowis still passing over the concave wall. The chlorine vapor bubbles areapproximately the same size as the pores in porous wall 36. The chlorinebubbles are subjected to a large shearing force as they enter thehigh-speed BHP layer. The shearing force distorts the chlorine bubblesand helps result in a large contact surface area. The liquid-gas contactsurface area according to the invention is significantly higher than inprior art SOG devices. The chlorine and BHP react and produce O₂(¹Δ) inthe liquid, or frothy, layer. According to the invention, it is notnecessary to add any diluents, such as helium, to SOG 14, althoughdiluents may be added.

The singlet delta oxygen forms vapor bubbles. Because of their lowdensity relative to the liquid solution, the bubbles experience asignificant pressure gradient, or buoyancy force associated with thecentrifugal force of flow along concave wall 30, that is transverse toconcave wall 30. This buoyancy force causes the low-density vaporbubbles to depart the aqueous solution on the side of the liquid, orfrothy, layer opposite from where the chlorine vapor enters throughporous wall 36. The centrifugal force also permits SOG 14 to operate ina zero-gravity or low gravity environment. This arrangement incombination with the high percentage utilization of up to 100% or nearly100% of the chlorine in the BHP-chlorine reaction, results in little, ifany, chlorine contamination of the O₂(¹Δ) stream. The O₂(¹Δ) streamdeparts SOG reaction chamber 28 through laser nozzle throat 24. A smallpercentage may leave through an outlet or exhaust duct. The laser nozzleis preferably a converging/diverging supersonic nozzle including a meansfor injecting iodine into the O₂(¹Δ), such as that described in U.S.patent application Ser. No. 60/410,857 filed by Applicant on Sep. 13,2002. Iodine feed and injections systems are not depicted in FIGS. 1-2.

Many factors control the rate at which the O₂(¹Δ) departs the liquidsolution to exit through nozzle throat 24. As the reactants pass throughSOG 14 very quickly, it is important that the O₂(¹Δ) depart the liquidsolution quickly so that it does not remain entrained in the solution asthe solution is exhausted to the collection tank 22. These factorsinclude the injected thickness of the BHP layer, the injection speed ofthe BHP, the average pore size in porous wall 36, the radius ofcurvature of concave wall 30, which is nominally around 2.5 cm (1 in),the angular extent of concave wall 30, which is preferably less than160° in extent, and the pressure inside reaction chamber 28. Thesefactors are chosen iteratively, in conjunction with other design andperformance constraints as will be understood by those of ordinary skillin the art. For instance, sintered metal porous sheets are available ina range of thicknesses with a range of average pore sizes. As theaverage pore size decreases, the pressure change, for a given flow rateof chlorine, across the porous wall increases.

As soon as most, or all, of the generated O₂(¹Δ) has departed the BHPsolution, the spent solution is removed from reaction chamber 28 bymeans of an exhaust duct or outlet 20. The spent solution is comprisedof salt byproducts (KCl or NaCl), a small quantity of KOH or NaOH basedions and excess H₂O₂. It is preferred to remove the spent solution asquickly as possible with a smooth inlet for exhaust duct 20 that avoidssplashing or aerosol formation that could contaminate the O₂(¹Δ) vaporstream. A suction pump in the exhaust may be used, if necessary, toassist with removal of the spent solution. The spent solution is storedin collection tank 22 for proper disposal; no BHP regeneration orrecycling system is needed according to the invention.

The salt generated by the BHP-chlorine reaction remains dissolved in thehighly dilute aqueous solution. The high-speed aqueous solution passesthrough reaction chamber 28 very quickly, preferably in fewer than about20 milliseconds, more preferably in fewer than about 10 milliseconds,and most preferably in fewer than about 5 milliseconds. Inside reactionchamber 28, the temperature of the liquid increases due to exothermicreactions with the chlorine. Because the BHP solution contains addedwater and is cooled before it enters the reaction chamber, the magnitudeof the temperature in the reaction chamber is minimized. A finite amountof time is required for the water vapor partial pressure to reach itsequilibrium value with the post-reaction temperature of the aqueoussolution. As the reactants pass through reaction chamber 28 veryquickly, there is insufficient time for the evaporation of liquid waterto establish an equilibrium value for the water vapor at thepost-reaction temperature, in the singlet delta oxygen exhaust stream.This factor, in combination with the reduction of the vapor pressure ofthe water by the solute, and the few milliseconds that the high-speedsolution is located inside the reaction chamber, results in a lowcontamination level of the O₂(¹Δ) gas stream with water vapor. Accordingto the invention, it is not necessary to use a water vapor trap prior tolaser nozzle 24; however, a water vapor trap may be used if desired.

Preferably, the O₂(¹Δ) stream is substantially free of any contaminants,such as water vapor and chlorine vapor byproducts, at the inlet of thelaser nozzle without any further processing, such as a water vapor trap,between the time the O₂(¹Δ) exits the reactant solution and enters thenozzle inlet. At the nozzle inlet, the O₂(¹Δ) stream preferablycomprises about 70% yield or greater singlet delta oxygen, and morepreferably comprises about 85% or greater, and most preferably comprisesabout 90% or greater singlet delta oxygen. Additionally, without havingpassed the O₂(¹Δ) stream through a water vapor trap, the O₂(¹Δ) streampreferably comprises less than about 15% water vapor at the nozzleinlet, and more preferably comprises less than about 10% water vapor atthe nozzle inlet, and most preferably comprises less than about 5% watervapor at the nozzle inlet.

The pressure in reaction chamber 28 refers to the gaseous pressure ofthe O₂(¹Δ) plus the gas-phase byproducts, i.e., the total pressure. Itwould also include the pressure of diluent; in this invention diluent isnot utilized, although it could be. Of the byproducts in chamber 28, themole fraction of H₂O and Cl₂ is small. The amount of O₂(³Σ) and O₂(¹Σ)depends on the yield. With a high yield, say 85% or more, the bulk ofthe gas is O₂(¹Δ).

The pressure in reaction chamber 28 may be as high as about 760 Torr (1atmosphere), or even up to about 910 Torr (1.2 atm) or higher, withoutthe addition of any diluent gases. For the use of SOG 14 to feed a COIL,the reaction chamber pressure is more preferably around 100 Torr to 400Torr (0.13 atm to 0.52 atm). This pressure range for a COIL SOG alsoassists in the departure of the O₂(¹Δ) from the liquid solution, ascompared to a significantly higher reactor pressure. These elevatedpressures would result in collisional deactivation of the O₂(¹Δ) to thepoint where the gaseous stream no longer yields efficient laser actionin prior art SOGs. Because of its compact, two-dimensional scalableconfiguration the SOG 14 according to the invention is preferably partof a plenum wall that directly feeds a converging/diverging nozzle of alaser. The O₂(¹Δ) generated in the BHP-chlorine reaction along theconcave wall 30 need only travel a few centimeters, preferably about 10cm (3.94 inches) or less, after departing the BHP-chlorine solution,which is preferably less than about 15 mm thick along concave wall 30,to reach the throat of the laser's nozzle 24 in the preferredembodiment. As seen in FIG. 2, nozzle throat 24 is preferably locatedopposite curved wall 30, such that the distance between curved wall 30and nozzle throat 24 is less than about 10 cm or less. Consequently,O₂(¹Δ) vapor is at an elevated pressure for only a few milliseconds, anddoes not have time to collisionally deactivate to any significantextent. The reduction in contaminants in the O₂(¹Δ) stream and the closeproximity of the SOG to the laser nozzle in the preferred embodiment ofthe invention make it feasible to produce O₂(¹Δ) at an elevatedpressure.

A SOG according to a preferred embodiment of the invention yields O₂(¹Δ)at a higher rate than prior art SOGs. Due to deactivation while theO₂(¹Δ) is dissolved in the BHP solution, deactivation of walls and thedimol and pooling reactions for O₂(¹Δ), the yield of O₂(¹Δ) at thethroat of a laser nozzle does not exceed about 50% in most prior artdevices. Higher yield values are often cited for prior art devices, butthese are upstream of the laser's nozzle throat. The dimol and poolingreactions are the dominant deactivation mechanisms and have driven priorart SOG systems to operate at low partial pressures for the O₂(¹Δ).However, according to the invention, deactivation of O₂(¹Δ) according tothe other mechanisms is reduced. For instance, the O₂(¹Δ) rapidlydeparts the BHP solution inside the reaction chamber, there is no needfor a water vapor trap, and the generated O₂(¹Δ) need only travel ashort distance to the laser nozzle's throat. These factors allow a SOGaccording to the invention to operate at high pressures while stillresulting in a yield as high as 70% or greater.

In addition to operation at a high pressure and with improved yield, theSOG according to the invention has a number of additional majoradvantages over prior art SOG devices. These include: (1) it isscalable, (2) it can operate in a zero-gravity or low gravityenvironment, (3) no added diluent or buffer gas is used, (4) thechemicals are efficiently utilized and (5) the O₂(¹Δ) stream issubstantially free of chlorine and water vapor contamination.

A SOG according to the invention was developed and tested in afeasibility experiment. A description of the test apparatus used in thefeasibility experiment, and as depicted in FIGS. 3 and 4, and theresults of the feasibility experiment are described below. Detailsregarding the amounts of reactants used, flow rates, part sizes, etc.described herein are illustrative of the preferred values for operationof a test-scale SOG in the feasibility experiment and do not limit thescope of the invention as claimed. Additionally, some details of the SOGand chemical supply systems and their methods of use in the feasibilityexperiment, including various gauges, fittings, piping, etc. are wellknown in the art, and as such are neither shown nor described.

FIG. 3 is a schematic diagram of a SOG system, including BHP andchlorine feed systems, according to a feasibility experiment for thepresent invention. The test apparatus consists of a BHP preparationsystem 46, a BHP feed system 56, a chlorine feed system 42, a SOGreactor 38, an exhaust system 84 for the generated O₂(¹Δ) gas, and anexhaust system 70 for the spent aqueous solution. The test materials arehigh-pressure nitrogen, a liquid nitrogen dewar, 30% aqueous H₂O₂, 45%aqueous KOH, liquid chlorine, distilled water, and tap water. Allmaterials are commercially available.

Water/nitrogen preliminary flow tests are first performed with nitrogenreplacing chlorine and water replacing BHP. High-pressure nitrogen fromnitrogen gas tank 40 is used to purge chlorine line 42 and tap waterflows through BHP line 44 to perform this preliminary flow test.

BHP is prepared in a batch by first pouring distilled water into mixer46, after which an aqueous H₂O₂ solution is added from H₂O₂ tank 48.Aqueous KOH is then allowed to slowly drip into mixer 46 from KOH tank50. Both the H₂O₂ and KOH solutions are pre-cooled in a refrigerator.During mixing with the KOH, the contents of mixer 46 are cooled withliquid nitrogen from nitrogen tank 52. Liquid nitrogen flows through aheat exchanger 54 with vertical copper tubing for the cold nitrogen. TheBHP temperature is monitored during preparation, and the KOH drip rateis adjusted to avoid overheating the BHP solution.

After the BHP has been prepared, a positive displacement pump 56, inBHP. line 44 between mixer 46 and SOG 38, pumps BHP to SOG 38. Theliquid chlorine tank 58 includes an eductor tube, which provides liquidchlorine to a heater 60 that gasifies it. Chlorine vapor passes throughline 42 to SOG 38. The time duration of a test is determined by theamount of BHP that has been prepared and the flow rate of BHP during atest run.

FIG. 4 is a cross-sectional side view of a SOG 38 and particularlyreaction chamber 62 of SOG 38 according to a feasibility experiment forthe present invention. Side walls 64 of SOG 38 are 0.25-inch thick,clear acrylic plates with a number of slotted holes 66 that allow foradjustment of four aluminum inserts 68 that provide flow paths for theBHP and chlorine reactants. The width of the inserts 68 is 1-inch, andthe flow paths between side walls 64 are two-dimensional. The inlet andexhaust ducting, such as exhaust duct 70, is rectangular incross-section, but the transition to a circular configuration is easilyperformed. Thus, the 1-in dimension is readily increased to any desiredlength; which establishes the scalability of a SOG according to theinvention. The SOG 38 depicted in FIG. 4 is only slightly smaller thanthe actual test device. This verifies the compactness of a SOG accordingto the invention.

Chlorine vapor flows through a converging nozzle 72, entering reactionchamber 62 through a narrow two-dimensional slit, or throat 74. Althoughit is preferred to use a porous wall to inject the chlorine into thereaction chamber according to the invention, a nozzle configuration, asused in the feasibility experiment, may also be used. The BHP aqueoussolution flows downward through a converging nozzle 76, enteringreaction chamber 62 through a narrow, two-dimensional slit, or throat78. The chlorine vapor enters reaction chamber 62 shortly after the BHPsolution enters. The vapor and liquid mix and flow along aconcave-curved wall 80. The reactant solution impacts an angled wall 82that directs the liquid flow into an exhaust duct 70. A vapor exhaust84, for exhausting O₂(¹Δ) gas, is located on the top side of SOG 38. Thesolution exiting through exhaust 70 flows to a collection tank 86 (asshown on FIG. 3). A 1.5 hp motor is located in the lid of the collectiontank. The fan on the motor provides a small suction pressure thatassists the flow of the spent liquid out of SOG 38.

In a feasibility experiment for a SOG according to the invention, theBHP solution comprises a mixture of about 1 gallon (3.79 L) of distilledwater, 1 gallon (3.79 L) of 30% aqueous H₂O₂, and 0.8 gallons (3 L) of45% aqueous KOH. These volumes translate into H₂O₂, KOH, and H₂O molarratios of approximately 1:1:10, where the H₂O value includes the aqueousportions of the H₂O₂ and KOH solutions and the added water. In contrastto BHP solutions used in prior art SOGs, this BHP solution is dilute.

The H₂O₂ and KOH solutions are pre-cooled in a refrigerator to atemperature below 32° F. During BHP preparation, which took about 50minutes during the feasibility experiment, the BHP temperature islimited to a maximum value of 36° F. The BHP is preferably cooled notonly during its preparation, but further cooled, if necessary, to atemperature slightly above its freezing point before injection into thereactor. Anomalous freezing of the BHP solution that has beenproblematic in prior art systems does not occur according to theinvention due to the use of a relatively dilute BHP solution, such asused in the feasibility experiment. A test run begins within a fewminutes after BHP preparation is completed. For the feasibilityexperiment, positive displacement pump 56 is set for a BHP flow rate ofabout 1.7 gpm (6.4 L/min), which provided a run time of about 1.5minutes.

The slit 78 at the exit of BHP nozzle 76 is about 0.02 inches (0.05 cm),while the slit 74 at the exit of chlorine nozzle 72 is about 0.06 inches(0.15 cm). Vapor exhaust 84 is throttled such that the vacuum pressureinside reaction chamber 62, during the test, is only about 6-inches ofwater, or 0.21 psi, below the ambient atmospheric pressure. Thistranslates to a reaction chamber pressure of about 14.5 psi (750 Torr)without the use of any gaseous diluents, which is significantly higherthan typical prior art systems.

The presence of O₂(¹Δ) in SOG 38 in the feasibility experiment describedwas confirmed by a visual inspection through the clear side walls of SOG38. An intense red dimol emission confirmed that the reaction producedO₂(¹Δ). The emission was noted during the experiment immediately afterthe BHP and chlorine began mixing. This indicates the rapidity withwhich the reaction takes place.

In addition to the parameters of the feasibility experiment describedabove, nominal values for key parameters of a SOG according to theinvention are as follows. These values are not considered to beminimums, maximums, or optimum values and may be adjusted according tothe desired scale of the system. A 1 m (3.3 ft) depth for the SOGcoupled with a radius of curvature for the concave wall of 2.5 cm (1inch), a BHP nozzle throat of about 1 mm (0.04 in), a laser nozzlethroat height of about 1.58 cm (0.62 in) and a laser nozzle exit heightof about 9.8 cm (3.9 in). For a 1 m (3.3 ft) depth dimension, thechemical flow rates are: Weight % of Aqueous Mass Flow Rate, kg/sConstituent Solution (lb/s) aq. H₂O₂ 35 5.330 (11.751) aq. KOH 45 6.838(15.075) added H₂O — 12.54 (27.65)  Chlorine — 1.75 (3.76) 

An improved SOG and its method of use are described according to theinvention. It will be understood by those of skill in the art thatvariations in the components or arrangement of components described maybe made within the scope of the invention.

1. A singlet delta oxygen generator, comprising a chamber where at leasta basic hydrogen peroxide (BHP) solution reacts with chlorine to producesinglet delta oxygen, wherein chlorine is introduced into the chamberthrough a porous inlet.
 2. The generator of claim 1, wherein the chamberfurther comprises: an inlet for the BHP solution; and a curved wall overwhich the BHP and chlorine flow and react to produce singlet deltaoxygen, byproducts, and a spent reactant solution.
 3. The generator ofclaim 2, wherein the chamber further comprises: a singlet delta oxygenoutlet; and a spent reactant outlet.
 4. The generator of claim 3,wherein the singlet delta oxygen outlet comprises an inlet to a nozzlefeeding a laser cavity.
 5. The generator of claim 1, wherein thepressure in the generator is between about 100 Torr to about 760 Torr.6. The generator of claim 1, wherein the generator further comprises acooling system for cooling the BHP solution to a temperature betweenabout 5° C. and about 10° C. above its freezing point prior to theinlet.
 7. The generator of claim 1, wherein the chlorine molar flow rateis about 70-120% of the molar flow rate of the BHP solution.
 8. Asinglet delta oxygen generator, comprising: a cooler for cooling a BHPsolution; and a chamber, wherein reactants, including BHP solution andchlorine, pass through the chamber at a predetermined rate to produce asinglet delta oxygen stream having a reduced water vapor concentration.9. The generator of claim 8, wherein the chamber further comprises: aninlet for the cooled BHP; and a concave wall over which the cooled BHPsolution and chlorine flow and react to produce singlet delta oxygen,byproducts, and a spent reactant solution.
 10. The generator of claim 9,wherein the chamber further comprises: a singlet delta oxygen outlet;and a spent reactant outlet.
 11. The generator of claim 10, wherein thesinglet delta oxygen outlet comprises an inlet to a nozzle feeding alaser cavity.
 12. A generator of claim 8, wherein the pressure in thegenerator is between about 100 Torr to about 760 Torr.
 13. The generatorof claim 8, wherein the cooler further comprises cooling the BHPsolution to a temperature between about 5° C. and about 1° C. above itsfreezing point prior to the inlet.
 14. The generator of claim 8, whereinthe chlorine molar flow rate is about 70-120% of the molar flow rate ofthe cooled BHP solution.